The residency admissions process is a high-stakes assessment system with the purpose of identifying applicants who best meet standards of the residency program and the medical specialty. Prior studies have found that professionalism issues contribute significantly to residents in difficulty during training. This study examines the reliability (internal structure) and predictive (relations to other variables) validity evidence for a standardized patient (SP)-based Professionalism Mini-Evaluation Exercise (P-MEX) using longitudinal data from pediatrics candidates from admission to the end of the first year of postgraduate training.